Conventional hard disk drives are the most widely used devices for data storage today. Some disk drives typically operate with two or more spinning disks and a pivoting head stack assembly (HSA). The HSA has multiple actuator arms. Attached to one end of each actuator arm are one or two suspension assemblies. Each suspension assembly includes a load beam, a flexure, and a slider. The flexure attaches the slider to the load beam. The slider carries a read/write transducer (i.e. head) for reading data from and writing data to the spinning disks.
An electromagnetic actuator such as a voice coil motor, controls movement of the HSA. During operation of the disk drive, the actuator moves the HSA and heads to selected disk tracks to access or store data.
Data storage density is measured in bits per unit area of a storage surface. Increases in data storage density has been achieved by a combination of increased track density (increasing the number of tracks per inch along the radius of the disk) and increased linear bit density (increasing the number of bits written along a track).
High precision actuators are now required to move the read/write head between the increasingly closely spaced data tracks. One promising approach is a dual-stage servo system, which uses a conventional voice coil motor as a primary (coarse low-bandwidth) actuator, and a piezoelectric micro-actuator as a secondary (fine high-bandwidth) actuator. High precision actuators, combined with improved head technology have enabled higher data transfer rates and higher storage density.
Higher data transfer rates, however, require increased bandwidth for transmitting read and write signals between the head and the front-end electronics of the disk drive. The bandwidth of a magnetic data storage device depends on the components in the recording channel, i.e. the electronics, interconnects, heads and recording media.
One limitation to increased bandwidth is signal noise. Particularly, the signal-to-noise ratio for data communicated by head leads on the load beam may not be optimized for additional data throughput. U.S. Pat. No. 5,055,969 to Putnam, for example, attempts to optimize the signal-to-noise ratio by placing a signal amplifier closer to the heads. More particularly, Putnam places an amplifier on the actuator arm. Accordingly, signals are pre-amplified prior to communication along the actuator arm. This optimizes the signal-to-noise ratio and enables increased throughput to the front-end read/write circuitry of the disk drive.
Another development in the effort to increase bandwidth is placing split pre-amplification circuitry on the load beam. This further optimizes the signal-to-noise ratio. Split pre-amplification circuitry divides standard read/write circuitry mounted on a head stack assembly into two or more sections including a mother chip and at least one daughter chip mounted on the suspension assembly. The daughter chips permanently couple with head traces and may perform any of a number of functions including signal amplification.
One drawback to making a coupling of the split pre-amplification circuitry, and other circuitry coupled to the suspension assembly, is that the suspension assembly may need to be removed from the actuator arm and reworked during assembly. Rework is routinely employed to precisely align the heads, assure targeted gram loads, meet flying height specifications, fix electrically defective heads, and/or replace mechanically defective components. Removal of the suspension assembly can result in a perfectly good split pre-amplification chip being discarded. Rejecting perfectly functional components is wasteful. What is desired is a way of rejecting only defective components and a way of preserving functional components during suspension assembly and HSA assembly.
Disk drive assembly includes other problems stemming from the non-compatibility of various head lead polarity and lead layouts with read/write circuitry configurations. Some sliders have four bonding pads. Two bonding pads couple with a read sensor of the head and two bonding pads couple with a write element of the head. An interconnect bonds to the slider bonding pads. The interconnect has two write traces and two read traces. Each read trace has a predetermined polarity, as does each write trace. The polarity of these head traces must be compatible with the read/write circuitry interface to enable the traces to couple with either a split signal pre-amplification circuit, or with the front-end read/write circuitry when a split pre-amplification circuit is not required.
Polarity compatibility between the heads and the read/write circuitry is critical for hard disk drive electronics. Head design and read/write circuitry design are often accomplished independently, possibly by different companies. This may result in polarity discrepancies and configuration variances between the two connection members. Electrical and magnetic testing are performed on a suspension assembly during assembly. Each test requires set-up (both hardware and software). The set-up configuration depends on the polarity of the read/write head to be tested. What is desired a universal-testing set-up that can be used on any suspension assembly regardless of the head polarity configuration.